BOAT HULL DESIGN 2-9 



can be used to perform the same functions. The 1-1/2 ounce mat is easier to drape and to 

 wet out with resin, but is less effective in increasing thickness and masking the weave of 

 the woven roving. 



The plies of woven roving provide the bulk of the laminate thickness, strength, and 

 impact resistance. The number of plies used depends on the strength required for the 

 particular laminate. Woven roving is used here because it is cheaper and requires fewer 

 plies than cloth, and has better impact resistance than mat. 



An interior layer of cloth may be added for appearance only, if desired. 



The second laminate, Type B, consists of: 1 ply of 10 ounce cloth on the outboard side, 

 a varying number of plies of mat and 1 ply of woven roving on the inboard side. 



Considering the laminate in detail: The outboard ply of cloth performs the same function 

 as in Type A laminate. 



The plies of mat provide the thickness and strength of the laminate. The number of 

 plies used depends on the strength required. 



The interior ply of woven roving is used to provide resistance to impact from objects 

 such as logs. 



An interior ply of 10 ounce cloth may be added if desired. 



The third laminate, Type C, is identical to Type B except that two layers of woven roving 

 are used instead of one. Each component performs the same function as before. The reason 

 for the additional ply of woven roving will be discussed later. 



It is sometimes stated that the material with good tensile properties should be placed on 

 the inboard face of the hull laminate because this is the "tension side". In this manual it is 

 recommended that woven roving be placed on the inboard side„ for resistance to impact from 

 objects, as distinguished from water impact. Fig. 2-10, indicating the deflected shapes of 

 an unstiffened and stiffened hull laminate under water pressure loading on the outboard sides 

 of the hulls, shows that the outboard face of a hull laminate can also be in tension. There- 

 fore, the arrangement of laminate reinforcing components should be made to provide for 

 tension on the outboard face as well as on the inboard face. The layer of 10 ounce cloth on 

 the outboard side of the laminates previously discussed performs this function. If required, 

 this portion of the laminate may be increased for higher strength. 



Loading due to impact from an object places a concentrated rather than a distributed 

 load on the laminate. For the unstiffened hull this change does not change the character of 

 the deflection curve. For the stiffened hull there is a considerable change since the load acts 

 on only one panel. This means that the loaded panel approaches the condition of simply sup- 

 ported edges rather than clamped edges as in the case with the distributed or pressure type 

 of load. In this case, the inboard side of the hull is in tension, and the woven roving is 

 placed there to resist this tension stress. 



As an aid in choosing a laminate, Figs. 2-1 1 and 2-12 have been prepared. Fig. 2-llisaplot 

 of material cost versus section modulus at the inboard face of the three laminates, Type A, B andC. 

 The figure shows that Type A laminate is relatively expensive but it is widely used on larger hulls 



